Image sensors convert optical light to electrical signals. Conventional image sensors are commonly used in electronic devices such as cellular telephones, computers, and digital cameras. Image sensors are formed from an array of photodetectors, each of which converts received light into an electrical signal. The effectiveness of a photodetector at converting received light into an electrical signal is the Quantum Efficiency (QE) of the photodetector.
Conventional image sensors are formed at two separate fabrication plants. The conventional image sensor is initially processed at a plant that uses complementary metal-oxide-semiconductor (CMOS) transistor fabrication techniques. The conventional image sensor is then sent to a color filter array (CFA) plant.
At the CMOS plant, photodiodes that convert light into electrical signals are manufactured in a silicon substrate. Interconnect layers used for wiring transistors are fabricated on top of the photodiodes and the substrate. Above the interconnect layers, a passivation layer that insulates the transistors and interconnect layers from external contamination is then deposited. When the CMOS process is complete, the conventional image sensor is transferred to the CFA plant for additional processing.
At the CFA plant, a color filter array is formed on top of the passivation layer. The color filter array includes tiles incorporating various colored dyes for color filtering. An example of a CFA pattern that may be used is the GREG (green-red-blue-green) Bayer pattern. After the color filter array is in place, an array of microlenses is formed on top of the color filter array.
A disadvantage of a conventional image sensor of this type is that the image sensor requires manufacturing processes that are implemented at two separate fabrication plants. This requirement can increase processing complexity and cost. Conventional image sensors may also be prone to contamination from the dye of the color filter array, which results in loss of efficiency, sensitivity, and reliability. It is desirable to provide improved image sensors.